How to Only allow numbers and a Minus "-" in a Textbox

Question

I would like to know how I would be able to allow only numbers and a "-" minus sign in a textbox?

Here is coding that I can already allow only numbers:

private void txtDicountSettlement_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    Regex regex = new Regex("[^0-9]+");
    e.Handled = regex.IsMatch(e.Text);
}

Answer 1

Just add the - to your regex character group, in a position that's not making a range of characters:

private void txtDicountSettlement_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    Regex regex = new Regex("[^0-9-]+");
    e.Handled = regex.IsMatch(e.Text);
}

Answer 2

I think you want something like this

^[0-9-]*$

It will match any digit any time and n no of dashes and will ignore any other character

Answer 3

[^-]+[^0-9]+ should prevent any input that's not an integer or a negative integer.

Answer 4

Add a preview text input event. Like so: <TextBox PreviewTextInput="PreviewTextInput" />.

Then inside that set the e.Handled if the text isn't allowed.

e.Handled = !IsTextAllowed(e.Text);

I use a simple regex in IsTextAllowed to see if I should allow what they've typed. In my case I only want to allow numbers, dots and dashes.

private static bool IsTextAllowed(string text)
{
    Regex regex = new Regex("[^0-9.-]+"); //regex that matches disallowed text
    return !regex.IsMatch(text);
}

If you want to prevent pasting of incorrect data hook up the DataObject.Pasting event DataObject.Pasting="TextBoxPasting" as shown here (code excerpted):

// Use the DataObject.Pasting Handler 
private void TextBoxPasting(object sender, DataObjectPastingEventArgs e)
{
    if (e.DataObject.GetDataPresent(typeof(String)))
    {
        String text = (String)e.DataObject.GetData(typeof(String));
        if (!IsTextAllowed(text))
        {
            e.CancelCommand();
        }
    }
    else
    {
        e.CancelCommand();
    }
}

Answer 5

private void textBox1_PreviewTextInput(object sender, TextCompositionEventArgs e)
    {

        if (!char.IsDigit(e.Text, e.Text.Length - 1))
        {
            if(e.Text.Length != 0 || (e.Text.Length == 0 && e.Substring(e.Text.Length - 1) != "-"))
                e.Handled = true;

        }
    }

Answer 6

Here is the best solution for numeric Textbox and This is answer by Answer!

    private bool IsOKForDecimalTextBox(char theCharacter, TextBox theTextBox)
{
    // Only allow control characters, digits, plus and minus signs.
    // Only allow ONE plus sign.
    // Only allow ONE minus sign.
    // Only allow the plus or minus sign as the FIRST character.
    // Only allow ONE decimal point.
    // Do NOT allow decimal point or digits BEFORE any plus or minus sign.

    if (
        !char.IsControl(theCharacter)
        && !char.IsDigit(theCharacter)
        && (theCharacter != '.')
        && (theCharacter != '-')
        && (theCharacter != '+')
    )
    {
        // Then it is NOT a character we want allowed in the text box.
        return false;
    }



    // Only allow one decimal point.
    if (theCharacter == '.'
        && theTextBox.Text.IndexOf('.') > -1)
    {
        // Then there is already a decimal point in the text box.
        return false;
    }

    // Only allow one minus sign.
    if (theCharacter == '-'
        && theTextBox.Text.IndexOf('-') > -1)
    {
        // Then there is already a minus sign in the text box.
        return false;
    }

    // Only allow one plus sign.
    if (theCharacter == '+'
        && theTextBox.Text.IndexOf('+') > -1)
    {
        // Then there is already a plus sign in the text box.
        return false;
    }

    // Only allow one plus sign OR minus sign, but not both.
    if (
        (
            (theCharacter == '-')
            || (theCharacter == '+')
        )
        && 
        (
            (theTextBox.Text.IndexOf('-') > -1)
            ||
            (theTextBox.Text.IndexOf('+') > -1)
        )
        )
    {
        // Then the user is trying to enter a plus or minus sign and
        // there is ALREADY a plus or minus sign in the text box.
        return false;
    }

    // Only allow a minus or plus sign at the first character position.
    if (
        (
            (theCharacter == '-')
            || (theCharacter == '+')
        )
        && theTextBox.SelectionStart != 0
        )
    {
        // Then the user is trying to enter a minus or plus sign at some position 
        // OTHER than the first character position in the text box.
        return false;
    }

    // Only allow digits and decimal point AFTER any existing plus or minus sign
    if  (
            (
                // Is digit or decimal point
                char.IsDigit(theCharacter)
                ||
                (theCharacter == '.')
            )
            &&
            (
                // A plus or minus sign EXISTS
                (theTextBox.Text.IndexOf('-') > -1)
                ||
                (theTextBox.Text.IndexOf('+') > -1)
            )
            &&
                // Attempting to put the character at the beginning of the field.
                theTextBox.SelectionStart == 0
        )
    {
        // Then the user is trying to enter a digit or decimal point in front of a minus or plus sign.
        return false;
    }

    // Otherwise the character is perfectly fine for a decimal value and the character
    // may indeed be placed at the current insertion position.
    return true;
}

and Then Call This Function in the Key Press Event Like As

public void Allow_Only_Numeric(object sender, KeyPressEventArgs e)
    {
        try
        {

            TextBox textbox = (TextBox)sender;
            Console.WriteLine(textbox.Text);
            if(IsOKForDecimalTextBox(e.KeyChar,textbox) == true)
            {
                e.Handled = false;
            }
            else
            {
                e.Handled = true;
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);

        }